Chip cards are already employed on a large scale in the form of telephone cards, access authorization cards for cellular telephones, bank cards, etc. The energy supply and the data exchange between the card and external devices are effected with these cards via touch contact (galvanically) between metallic contact areas arranged on the card and corresponding contacts in the respective devices.
In addition to these contact-operated cards, so-called contactless cards are also increasingly employed where the energy supply and the data exchange of the integrated circuit of the card is effected inductively via a coil which is embedded in the card.
In the manufacture of contactless chip cards the coil must be embedded into the card body. To this end the coil, which is arranged on a coil carrier layer with its coil terminals, is laminated between the coil carrier layer and one or several card layers which are arranged above it.
The coil (conductor paths and coil terminals/large area coil ends) is preferably etched from an electrically conducting (preferably copper) coated plastic foil. Here, the plastic foil constitutes the coil carrier layer, or the plastic foil with the etched coil may be combined with another plastic layer to form the coil carrier layer. In alternative configurations, a wire wound coil is glued onto the coil carrier layer or partially pressed into same ultrasonically in order to locate it in its position. In a further embodiment the coil is applied to the coil carrier layer as an electrically conducting layer in accordance with the silk-screen printing method. It is also possible to apply the coil in the form of an electrically conducting layer in accordance with the hot embossing method.
Regardless of the embodiment of the coil and the way of applying it onto the coil carrier layer, a recess for accommodating a chip module which contains the integrated circuit (semiconductor element/chip) and which comprises metallic contacts for connecting the chip with the coil terminals is machined into the finish laminated card. This exposes the coil terminals so that the electrically conducting connection with the corresponding contacts of the chip module can be made by means of a conducting adhesive or a soldering material.
Thereby, however, serious drawbacks are encountered. When milling the recess, not only are the coil terminals exposed but also the coil windings/conductor paths extending between the coil terminals, i.e., if the coil comprises N number of windings, N-1 number of windings extend between the coil terminals. This leads to the following problems:
a) The conductor paths of the coil, which extend in the height of the coil terminals and which have a width of approximately 80 .mu.m only, tend to be damaged very easily or severed completely during milling so that the coil quality deteriorates or the coil is even destroyed totally. This is not so critical with the large area coil terminals (&gt;1 mm.sup.2) because in this case, a "scratch" has no consequences.
b) In the manufacture of an electrically conducting connection between the contacts of the chip module and the coil terminals an electric short circuit is easily caused between the conductor paths of the coil or between the conductor paths and the coil terminals, respectively, by the conductive adhesive or the soldering material due to the fact that the distance between the conductor paths and the distance between the conductor path(s) and the coil terminals is very small, thus rendering the coil useless. In most cases it is not possible to change the arrangement of the coil (conductor paths and coil terminals) on the coil carrier layer so as to increase the distances between the conductor path(s) which extend between the coil terminals in the area of the recess and the coil terminals, in order to prevent a short circuit because the coil carrier layer, is machined in a centre area between the coil terminals for the accommodation of parts of the chip module so that conductor paths in that area would be destroyed. In order to avoid short circuits to and between the conductor paths a solder blocking varnish would have to be applied in a labor and cost intensive manner, or an insulating layer would have to be applied to the conductor paths in a similarly labor and cost intensive manner. In this case, too, there is the problem that the coatings and the conductor paths themselves would be destroyed by milling.